Wednesday, July 6, 2011

Building a 30m Vertical in a Couple of Hours

As I like to get out and about I wanted something reasonably small and easy to carry for portable work, I came up with this simple solution for my 30 meter work.

1. Find a choc block connector (11 or more connectors) and attach by screwing it inside a small waterproof 100mm x 100mm plastic box, I used a spare 11 choc block connector which fitted snugly in my small box, but obviously the bigger the box the larger the connector.

2. Using some thick copper wire (20 gauge) I cut 9 x 1” inch lengths and bent each one in to a U shape and joined up 10 of the block connectors, this meant that 20 connectors were now electrically joined together to be used for ground radials connections.

3. Drill out 20 holes in the each side of the box (10 each side roughly aligned to each connector slot) then measure and cut 20 pieces of cheap multi strand telephone wire (minimum of 4 to a ¼ length) to use as ground radials. (Any wire will do, I had some telephone wire hanging about, the beauty being its 4 stranded so therefore quadrupling the wire).
Thread through and attached the radials to the 10 connectors of the choc box.

4. Take some antenna wire, (I found some spare copper flexi weave to use for the main radial) and cut to size for 30meters (approx 23 and 1/2’), drill a small hole at the end of the plastic box which has the remaining unused connector block, feed through the wire/flex and attached to one side of the remaining connector in the choc block.

5. Drill a final larger hole in the side of the plastic box in line with the wire antenna connector (this is for the coax).

All completed except for adding a few more radials; note that the top connector takes the centre coax wire and the antenna. The earth from the coax attaches to the second connector in from the top.
6. With the coax fed through attach the centre wire of the coax in to the choc block connector hole opposite the antenna wire and connect the brazed outer ground to one of the block connections holding a radial.
Fix a PL259 to the other end of the coax.
Close the box up.

7. Test and trim the antenna length accordingly.
Do not plug in to the radio without testing.

After screwing up the box up I took it out to the garden, laid out the ground radials and hung the antenna up in a tree, did a quick trim and check with an MFJ 259 to get a 1:4:1 SWR. Then connected up to the radio and was soon tapping out to a chap in Sicily who gave me a 599 with 10 watts. Isn’t Amateur Radio fun?

Incidentally, the beauty with this antenna is you can have various ground radials lengths to cover whatever band you choose. So by just inserting the correct antenna length you can quickly change frequency. I have two wire antennas set for 30 and 40 meters and with a minimum of 4 ground radials set for ¼ length of the lowest band.
With the ground radials and antenna rolled up I have a small portable antenna.
I also have a 9 metre fibre glass pole that I can break down in to 3 single metre lengths so I can hang the wire off a 9 metre pole if no trees are available.

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